Seedling pots or containers filled with growth medium such as peat or mixtures of peat and fibers and/or earth are used to germinate seeds and grow seedlings until they are large enough to be transplanted into the soil. The containers are often perforated in order to drain surplus water and to aerate the growth medium. The use of perforated containers makes possible the so called elevated growing, in which water and nourishment are sprinkled onto the upper surface of the containers which are supported in apertures of a plate or form depressions in this, whereas the walls and bottoms of the containers are situated in an airfilled space, which by so called air pruning will diminish the egress of roots through the perforations.
The seedlings may be transplanted either together with the perforated pot, which then must permit the passage of roots through the perforations and be easily ruptured by the roots, or the seedlings together with a lump of growth medium may be removed from the pot and transplanted as such into the soil.
The usual way to fill seedling containers is to fill dry growth medium in the containers, compact the medium and water it to an appropriate moisture.
In order to get a suitable pore space the dry growth medium must have a suitable structure and composition. E.g. when growing forest plants, usually peat or mixtures of peat and fibrous material are used. In order to get a correct air capacity the peat must be compressed so that it expands on wetting. For this purpose a special quality called chips-peat is produced. It consists of compressed granules of peat and is supposed to swell to the correct volume when watered.